Boiler condensate pipe regulations

Most modern boilers are high efficiency condensing boilers which use gas as a fuel to condense water vapour to create heat which is recycled back into your heating system. During this condensate process acidic wastewater is produced which exits the boiler via a small plastic pipe called a ‘boiler condensate pipe’.

In most cases, a boiler condensate pipe will exit behind the boiler through an external wall and connect to a drain. In some cases, it can be internally connected. If you are wondering what size pipe for boiler condensate is required, industry regulations and manufacturer installation instructions detail the minimum internal diameter required according to the discharge pipe location related to the boiler and external wall outlet.

For all connection scenarios there are also industry regulations specifying how to install pipes correctly in order to reduce the possibility of freezing. This is because frozen condensate discharge pipes will cause a boiler to shut down. To help prevent this - and to ensure you don’t inadvertently invalidate your boiler warranty - these boiler condensate pipe regulations should be followed, together with manufacturers’ instructions.

Naturally, the vast majority of cases, problems occur when the boiler condensate pipe is located externally for some or all of its length, and especially in extreme conditions such as prolonged sub-zero temperatures. However, extra measures can be taken to better protect your condenser boiler waste pipe from freezing. These include fitting boiler condensate pipe insulation that is a minimum thickness of 19mm class “O” grade PVC coated material and that is water- and weather-proof.

Another option includes fitting trace heating whereby an external thermostat can be fitted to the external boiler condensate pipe to raise the temperature of the pipe in freezing conditions. Trace heating takes the form of an electrical heating element run in physical contact along the length of the boiler condensate pipe.

A third option is fitting internal auxiliary (additional) high volume syphon unit inside the premises. The storage capacity of an auxiliary siphon increases the volume of condensate discharge reducing the risk of freezing.

With this knowledge you can check with your gas engineer that your boiler condensate pipe has been installed in line with current boiler condensate pipe regulations. This will take away the worry of your condenser boiler waste pipe freezing in Winter which would otherwise cause your boiler to stop working.

Frozen condensate pipes

How to prevent an external condensate pipe from freezing and easy fixes to remedy it if it does.


Know what you can do to restart your hot water supply and understand the key checks to make before bringing in an engineer to fix it.

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